Locking fasteners and locking fastener assemblies are used to prevent loosening of a threaded fastener in a fastener joint. There are many types of threaded joints in which loosening of a fastener is undesirable. One example to which the principles of the present invention may be applied is an axle assembly of a vehicle, including automobiles, trucks, trailers or other motorized craft.
In a typical axle assembly, axle bearings are supported between an axle or spindle and a wheel hub or spindle support to permit rotation of a vehicle wheel. An axle bearing nut is used to hold the components together. In order to prevent premature bearing failure, the nut must be installed properly to avoid excessive axial bearing load or, alternatively, excessive free play. In addition, after assembly it is important to prevent loosening of the axle bearing nut to avoid bearing failure or even dangerous loss of a wheel.
A conventional axle assembly includes a spindle with male threads having an axially extending slot. A washer received on the spindle has a tab in the slot to prevent rotation of the washer. After the nut is threaded onto the spindle and tightened to the desired degree, part of the washer is deformed to lock the washer to the nut and prevent further rotation of the nut.
This conventional approach has disadvantages. One serious problem, especially in original mass production, is that installation of the washer and nut requires too many manual assembly steps. Another disadvantage is that the washer must be deformed both after installation of the nut and again when it is desired to remove the nut. The fact that the nut and washer are separate pieces makes it possible for the assembly to be installed improperly, for example without the washer or with an incorrect or damaged washer. Moreover, the locking of the nut against rotation is not as positive as desired because the washer can be deformed or broken.
Another disadvantage of previous systems is that once the desired end play or bearing pre-load has been achieved, the inner nut or outer nut/locking washer/locking element must again be rotated. This additional adjustment is required to turn the elements clockwise or counter-clockwise in order to align and subsequently engage the locking element(s). This final movement to align and lock the components subsequently defeats the "final" pre-load or end play adjustment that has just been achieved. In essence, the lock nut system final adjustment is not final until this last adjustment is made.
Before the locking element can be engaged, however, the nut must be rotated clockwise or counterclockwise in order to align and engage the locking clip. In order to accomplish this final engagement, the application tool must be applied in order to deflect the locking clip, thus allowing the free rotation of the nut.
In order to overcome such disadvantages of the conventional assembly, it has been proposed to provide locking fastener assemblies in which a washer and a nut are normally locked against rotation and in which the installation tool or wrench can be manipulated to free the nut for rotation. Examples of such proposals can be found in U.S. Pat. Nos. 3,851,690 and 3,942,570. While the assemblies disclosed in these patents overcome some disadvantages of the conventional nut and washer, they are subject in turn to other disadvantages. They include relatively delicate mechanisms requiring complex movements and are not well suited to the types of forces and environments encountered by automotive vehicles. In addition, they require special manipulation of an installation tool or wrench over and above the normal use of a wrench with a nut.
Another prior approach has been to use a nut and a non-rotating retainer normally separated by a spring and having interfacing teeth or similar locking structures. As the assembly is tightened, the spring force is overcome and the nut becomes locked to the retainer to prevent further rotation. In addition to complexity and expense, the arrangement has the disadvantage that as the nut reaches its final position, it is not free spinning. The ragged, uneven torque characteristic interferes with the use of torque detecting equipment that could otherwise detect a predetermined degree of tightening of the fastener assembly. Also, this assembly requires at least the amount of pre-load necessary to compress the spring normally separating the nut from the retainer.
U.S. Pat. No. 4,812,094 discloses a free spinning positively locking fastener assembly for threaded joints such as automotive or truck wheel assemblies. That assembly includes a nut having a flange with a retainer washer captured on the nut flange. The washer includes a tab received in a slot of a wheel spindle to permit the washer to move axially and prevent the washer from rotating. A locking clip locks the nut to the washer to prevent rotation of the nut relative to the spindle. The locking clip is released by engagement of a wrench socket with the wrenching structure of the nut so that the nut can be threaded to a desired position. When the wrench socket is removed, a locking finger on the clip engages the washer to prevent the nut from rotating.
This locking fastener assembly has suffered from disadvantages. One disadvantage is that the locking clip according to U.S. Pat. No. 4,812,094 is located at a corner of the wrenching structure where two wrenching flats intersect. In automotive assembly operations, impact wrench drivers are used to install wheel fastener assemblies, resulting in wear of wrench sockets. The problem of socket wear is particularly acute for sockets that are formed from sheet metal rather than being forged, as is common in larger socket sizes. Socket wear results in deformation of the corners of the sockets such that a socket that remains effective for tightening the nut of the fastener assembly is nevertheless ineffective to release the locking clip located at a corner of the nut. If the clip is not released, the clip can be destroyed in the tightening or loosening operation, resulting in an installed wheel hub with the nut not locked and engaged with the retainer. This allows the nut to rotate on the spindle.
Another disadvantage of the known locking fastener assembly is that with the clip located at a corner of the nut, the nut engages the edges of the clip latch release segment. Contact with the edges is not as effective or as reliable as a firm face to face contact in the plane of the latch release segment.
Use of a single locking clip in accordance with U.S. Pat. No. 4,812,094 results in an arrangement wherein the locking function is dependent on a single component. In addition, a single resilient clip located between the nut and the retainer washer introduces an imbalance because the resilient clip tends to separate the nut and the washer at a single point around the periphery of the nut. Also, the single locking clip can only be positioned into one of the grooves, limiting the nut to one of N position, where N is the number of grooves.
To overcome the deficiencies of the use of a single clip a two clip system is disclosed in U.S. Pat. No. 5,597,278. The two locking clip system can only be positioned into one diametrically opposite grooves, limiting the nut to one of N positions. Where N is the number of grooves and before the locking clips can be aligned and engaged, the nut must be rotated, thus altering the end point or pre-load settings.